The present invention relates to a computerized process monitoring and control system and more particularly to a low level field programmable microprocessor-based system controller for providing control and energy management functions relative to a building heating, ventilating and air conditioning system.
Automated networks are widely employed in building environmental control systems for interconnecting remotely located heating, ventilating and air conditioning equipment, commonly termed HVAC equipment, with a central station to provide optimum comfort for the building occupants and for energy conservation. Hierarchical architecture is used to form such networks which are comprised of a main computer linked to lower level units by electrical trunk conductors. These trunk conductors may be of the dedicated type or may comprise conductors simultaneously used for other purposes such as telephone communications or the transmission of electrical power. Processing of the control and monitoring data and generation of command signals and the like advantageously employs computers which can rapidly and accurately service a large number of remote equipment units. For example, computers have been employed in heating, ventilating and air conditioning systems to monitor and regulate the positions of damper and valve actuators for controlling airflow and fluidflow in air handling units and to monitor the signal values of temperature and humidity sensors and regulate their related set points. Generally, such systems employ a main computer as a central processing unit having operator display and manual control functions as well as computational and command-generating capabilities. Additionally, the central processing unit embodies a library of computer software programs arranged in a relatively complex programmer language for providing energy management functions as, for example, temperature set back in office buildings during evening and weekend hours and for the limiting of total load demand. These central processing units are commonly termed headend units and are connected at the first or highest hierarchical level in a building automation system. Such headend units are often adapted to control and/or monitor several hundred or even several thousand individual datum points within the building system. The position of actuators used for damper and valve positioning and the output signals of temperature and humidity sensors used for providing feedback data relating to those parameters are examples of such datum points. Known systems or subsystems generally useful in the control of a building environment are shown in U.S. Pat. Nos. 3,400,374; 3,845,472, 4,042,780 and 4,159,470.
In addition to the central processing unit, such automated networks often employ a plurality of second level data processing units connected to the headend unit for performing certain tasks which would otherwise be required to be performed by the latter. As an example, a data processing unit may perform information checking functions with respect to signals passing between data points and the headend unit. Such data checking may include, for example, the detection of alarm signals or the detection of temperature changes which exceed predetermined values.
Each data processing unit may, in turn, have a plurality of third level field processing units coupled to it for performing analog to digital conversion and limited processing functions. Each field processing unit typically has connected in relatively close proximity thereto one or two sets of equipment having a relatively small number of individual datum points. Air handling units and water chillers are examples of such equipment. A variant field processing unit has limited standalone capability in that it incorporates software programming embodying default parameters which are activated only in the event the headend unit is disabled or in event of a trunk line fault, for example.
Air handling units, one of several types of environmental equipment to be monitored and controlled by a field processing unit, include ducts for controlling air flow to a conditioned space and heating and chilling coils disposed within the ducts for regulating the temperature of air being introduced into the space. Air handling units typically employ pneumatically or electrically actuator-operated shutters or dampers for controlling the flow of outside air to and from the conditioned space.
Additional actuators are provided for the manipulation of valves used to control the flow of fluid to the chiller and heater coils. Since digital signals from a field processing unit are often incapable of directly powering these actuators, it may be necessary to provide a separate, power amplifying and/or signal transducing equipment interface panel immediately adjacent each of the air handling units. These interface panels receive digital signals from the associated field processing unit and responsively provide pneumatic or electrical power at levels sufficiently high to position the actuators mechanically coupled to the dampers or valves. An example of a typical air handling unit for conditioning a space within a building is depicted in U.S. Pat. No. 4,263,931 while U.S. Pat. No. 4,261,509 illustrates an apparatus for controllably positioning a pneumatic actuator which is mechanically coupled to a damper of an air handling unit.
While systems of the aforementioned type are in wide use, they tend to be characterized by certain disadvantages. In particular, the headend central processing unit may be subject to periodic failures. In the event of a failure of a prescribed type, the entire building system or major portions thereof may be disabled. Additionally, the integrity or utility of the trunk conductors may be impaired by atmospheric electrical disturbances, failure of connected devices unrelated to the HVAC equipment control system, physical damage and the like. Unless the low level HVAC control and energy management units are capable of standing alone, i.e., of operating in the absence of a headend unit, whether by reason of equipment failure or control system design, and yet continuously performing those functions in an optimized manner, occupant discomfort and wasted energy may result. For example, while such data processing units are useful for detecting alarms or other default signals within the received signal information by it and for communicating those signals to the headend unit, they are frequently incapable of repetitively, algorithmically processing the information and generating commands or other signals based thereon. Field processing units of the described type have limited utility in that they contain no computer programs, either in single or selectable library arrangement, for continuously performing optimized control functions in a standalone mode or for permitting a local operator to select and modify an aspect of a program routine to meet the requirements of locally-changed environmental conditions. Another disadvantage of field processing units of the known type is that their control capability is frequently degraded when functioning in a standalone mode by reason of the failure of equipment related to the headend unit. That is, they are configured to retain actuator positions at settings which existed immediately preceding a fault rather than to continue to monitor and control positions for optimized energy management and occupant comfort.
Computer programming incorporated in headend, data processing or field processing units is usually configured in a relatively complex format requiring the services of an experienced, highly trained programmer for modification thereof. As a result, it is difficult or impossible for a relatively untrained user to modify data established in the programming in order to adapt the system to changed requirements.
Yet another disadvantage of systems of the known type is that they usually require a duplication of sensors at the individual datum points. For example, an air handling unit pneumatic interface panel may require that a temperature feedback sensor be disposed in an air duct to provide temperature-related information in the form of a pressure signal which is proportional thereto. The pneumatic interface panel will compare the temperature set point pressure signal received from the field processing unit with the pressure signal received from the temperature sensor, process the information by executing an analog algorithm and selectively change a damper position, depending upon whether an error exists. On the other hand, a sensor which emits a voltage signal proportional to temperature will be required to be installed in an air duct to provide temperature feedback to the headend central processing unit for performing the energy management function established therewithin.
A digital, microprocessor based control and energy management system which has a library of locally selectable, mnemonically identified computer program routines embodied therein and which permits operator modification of aspects of those routines, which combines certain functions of the central processor, the field processing unit and the equipment interface panel for low level distributed processing of information, which is capable of continuous standalone optimized control and energy management functions, which is capable of digital algorithmic execution and of direct digital control of actuators and which avoids the necessity of certain sensor duplicity would be a significant advance over the prior art.